This invention relates to a pressure developing device suitably used for generating a visible image on a developing sheet by pressurizing a photo and pressure sensitive recording sheet on which a latent limage is formed by exposure and the developing sheet in a state that both the sheets are overlapped.
A transfer type image recording medium is disclosed as already known, for example, in Japanese Patent Provisional Publication SHO58-88739U.S. Pat. No. 4,399,209 and the like. This transfer type image recording medium is composed of a photo and pressure sensitive recording sheet coated with a plurality of microcapsules containing dye precursor, photosensitive resin, photo polymerization initiator and the like and a developing sheet coated with a developing agent to cause a color developing reaction with the dye precursor.
With the image recording medium, the photo and pressure sensitive recording sheet is exposed based on image data supplied from an original, the developing sheet is overlapped on the exposed surface of this photo and pressure sensitive recording sheet and both the sheets are pressurized, whereby the microcapsules remaining unhardened on the photo and pressure sensitive recording sheet are crushed to enable the dye precursor contained therein to cause the color developing reaction with the developing sheet so that a visible image is generated on the developing sheet. This pressure developing, however, requires large pressure force for crushing the microcapsules.
Thus, a pressure developing device for this kind of the image recording medium employs a pair of backup members (usually each composed of a plurality of backup rollers) are brought into contact with a pair of pressure rollers respectively disposed behind them.
When, however, the backup member brought into pressure contact with the pressure roller on the side of the developing sheet has less rigidity smaller smaller than that of the backup member brought into pressure contact with the pressure roller on the side of the photo and pressure sensitive recording sheet, the pressure roller on the side of the developing sheet is greatly bent to cause the developing sheet to be curved to a concave shape and wrinkled and then image quality is deteriorated when the photo and pressure sensitive recording sheet and the developing sheet are passed between the pressure rollers in the overlapped state.
Further, when pressure force is uniformly imposed between the pressure rollers in the axial direction thereof or larger pressure force is imposed on the opposite sides of the pressure rollers, both the pressure rollers are bent to reduce the pressure force at the central portion thereof and then contraction force directed to the center of the axial direction of the pressure rollers is imposed on the developing sheet to cause it to be wrinkled with a result of the deterioration of the image quality when the photo and pressure sensitive recording sheet and the develping sheet are passed between the pressure rollers in the overlapped state.